The present invention relates to methods and components for making microelectronic assemblies. Complex microelectronic devices such as modern semiconductor chips require numerous connections to other electronic components. For example, a complex microprocessor chip may require many hundreds of connections to external devices.
As disclosed in U.S. Pat. No. 5,518,964, the disclosure of which is also incorporated by reference herein, flexible connections can be provided between microelectronic elements using a process in which the leads are connected between the elements and the elements are then moved through a predetermined displacement relative to one another so as to deform the leads. For example, a first element may be a microelectronic connection component which includes a dielectric element such as a flexible sheet having a bottom surface. A plurality of leads are also provided. Each lead has a terminal end permanently attached to the dielectric element and a tip end remote from the terminal end. Each lead initially extends in a horizontal plane, generally parallel to the bottom surface of the dielectric sheet. Desirably, the tip ends of the leads are releasably connected to the dielectric element. While the leads are in this condition, the tip ends are attached to a second element, such as a further dielectric sheet, a semiconductor chip, a semiconductor wafer or other microelectronic element. After the tip ends of the leads have been attached to the second element, the first and second elements are moved away from one another, so that the tip ends of the leads are pulled away from the first element and bent to a vertically extensive configuration. In this condition, the leads are flexible and allow movement of the first and second elements relative to one another. Preferably, a curable liquid material is introduced between the elements to form a compliant layer therebetween. Thus, in the completed assembly the first and second elements are movable relative to one another.
As further described in the ""964 patent, these arrangements offer numerous advantages. The resulting assembly provides mechanical decoupling between the elements, and thus provides compensation for thermal expansion and warpage of the elements. The preferred processes according to the ""964 patent can make a large number of connections in a single operation. For example, where a wafer incorporating numerous chips is used as one element in the connection process, all of the leads to all of the chips can be connected in a single set of operations. The resulting wafer-scale assembly can be severed to provide numerous individual units, each including one or more chips. Further variations, improvements and adjuncts to the processes and components taught in the ""964 patent are also disclosed in U.S. Pat. No. 5,688,716, and in copending, commonly assigned U.S. patent applications Ser. No. 08/532,528 Filed Sept. 22, 1995; Ser. No. 08/678,808 Filed Jul. 12, 1996; and Ser. No. 08/690,532 Filed Jul. 31, 1996, the disclosures of which are also incorporated by reference herein.
Despite the advances in the art discussed above, still further improvements would be useful.
One aspect of the present invention provides methods of making a microelectronic assemblies. A method in accordance with this aspect of the invention desirably includes the steps of providing a pair of elements having a plurality of signal leads attached to said elements and electrically interconnecting said elements, and also having a plurality of straps attached to said elements, said signal leads and said straps extending generally in a horizontal direction. The method further includes the step of moving the elements vertically away from one another so that said straps and said signal leads are bent to a vertically extensive disposition. In the moving step, the straps at least partially constrain movement of the elements relative to one another. However, the signal leads most preferably do not constrain this movement. Stated another way, the straps control the relative movement so that the signal leads are not pulled taut and placed under tension between the elements. Accordingly, little stress is applied to the relatively delicate signal leads and their connections to the microelectronic elements. The straps may be considerably stronger than said signal leads. The straps may also be shorter than the signal leads so that as the elements move away from one another, the straps will be pulled taut before the signal leads. Typically, the straps are less numerous than the signal leads.
The straps may also be electrically connected to the microelectronic elements so that the straps further electrically interconnect the elements. In a particularly preferred arrangement, the elements include constant-potential connections such as power or ground connections and some or all of the straps are electrically connected between constant-potential connections on both of said elements. Thus, the straps may serve as power leads, ground leads or both in the finished assembly.
The elements may include opposed, horizontally-extending surfaces of said elements confronting one another and the signal leads and said straps may be disposed between these opposed surfaces. For example, one of the elements may be a connection component including a structure such as a dielectric sheet having a bottom surface, whereas the second element may include one or more semiconductor chips having top surfaces with contacts thereon. The leads and straps may be provided on the bottom surface of the connection component, so that the leads and straps extend along the bottom surface of the connection component, and the connection component may be positioned with the bottom surface facing the top surfaces of the chips. The leads and straps may be connected between the elements by bonding ends of the leads and straps to the top surfaces of the chips.
Each strap may have a first end connected to a first one of the elements and a second end connected to a second one of the elements. Before the moving step, the second end of each strap may be offset from the first end of that strap in a first horizontal direction. In this arrangement, the straps will constrain the first element to move relative to the second element in the first horizontal direction during the moving step. Each signal lead may also have first and second ends connected to the first and second elements, respectively. Prior to the moving step, the second end of each lead may be offset from the first end of the lead in the first horizontal direction. Thus, the movement of the first element with a component of motion in the first horizontal direction will cause the ends of each said signal lead to move horizontally towards one another while the lead ends move vertically away from one another as the elements move away from one another. Where the signal leads are initially straight, this compound movement can bend the leads into a generally S-shaped configuration.
The step of moving the elements vertically away from one another may include the step of applying a fluid under pressure between opposed surfaces of the elements so that the fluid forces the elements away from one another. Because the movement of the elements relative to one another is constrained by the straps, there is no need to use external mechanical elements to control the movement.
A further aspect of the present invention provides connection components for making microelectronic assemblies. A connection component according to this aspect of the invention desirably includes a structural element, and a plurality of flexible signal leads, each such lead having a fixed end permanently attached to the structural element and a free end detachably secured to the structural element. The component also includes a plurality of flexible straps. Each strap has a fixed end permanently attached to the structural element and a free end detachably secured to the structural element. Most preferably, the straps are shorter and stronger than the leads, and the straps are disposed adjacent the leads. The structural element may have a surface with the straps and the leads extending along the surface. The straps and the leads desirably are disposed in an array on the bottom surface and the leads are interspersed with the straps in the array. The structural element may be a dielectric element such as a flexible dielectric sheet or may be a semiconductor chip or wafer.
As discussed above in connection with the method, the free end of each the lead may be offset from the fixed end of that lead in a first horizontal direction along the bottom surface, and the free end of each the strap may be offset from the fixed end of that strap in the same first horizontal direction. Components in accordance with this aspect of the invention may be used in methods as discussed above.